Pneumatic brake systems which use pressurized air to operate the service brakes and also to release the parking or safety brakes, are well known in the art. The pressurized air (so-called “supply pressure”) is stored in a reservoir that is charged by a compressor through a series of check valves and/or a pressure protection valve. In these pneumatic brake systems, the driver's brake pedal or other controls directs the flow of so-called “control air.” The brake pedal, when applied, opens the reservoir air supply and sends control air, which generates control air pressure, to a relay valve. The relay valve, in response to the control air pressure, connects the reservoir air supply to the brake actuators, which applies mechanical force to the brakes.
In these braking systems, the pressure generated by the driver's foot on the pedal is not applied directly to the brakes; rather, it is used to deliver air pressure from the reservoir to the brake actuators, which then apply mechanical force to the brakes. While the vehicle is in use, the supply air pressure remains at a high level. It may fluctuate somewhat, but it generally remains above 90 psig (pounds per square inch, gauge). When the mechanical parking brakes of the vehicle are needed and the pneumatic brakes are no longer needed, the brake system is normally de-pressurized and the supply line air pressure drops to zero psig (or atmospheric pressure), thus resulting in automatic application of the vehicle parking brakes and, as a result, the application of the spring brake component.
This depressurization step is typically accomplished on school buses and commercial vehicles by “pumping down” the brakes to relieve the pressure below a certain preset value. This procedure is done both when starting up the vehicle as a test to determine if the brake system's compressed air system is functioning properly (i.e., no leaks) and also to ascertain whether the parking brake is functioning properly (as it engages below a certain psig as a result of the application of the spring brake component). Additionally, many states, for safety reasons, require that any time a driver leaves a commercial vehicle, most particularly school buses, the parking brake must be engaged by pumping down the brakes rather than simply mechanically engaging the parking brake; this safety requirement is required by states due to the fact that a mechanically engaged parking brake can be disengaged given that air pressure is still present in the overall braking system, whereas one which has been engaged by a reduction in compressed air below a certain level cannot, as it follows that there is no air pressure left in the system to release the spring brake component.
One potential harmful effect of this “pumping down” of air brakes procedure is that unwanted oil and moisture can be distributed throughout the entire air system, causing premature failure of the air valves. Additionally, the strong mechanical force associated with the pumping of brakes down to release or reduce the compressed air can also contribute to premature brake component failure.
Referring now to FIG. 1, disclosed therein is a schematic diagram of a standard prior art air brake system 100. The system 100 includes a compressed air system source 111 and a compressed air system 110 in communication with the compressed air system source 111. The compressed air system 110 is comprised of a supply (or wet) reservoir 112 in fluid communication with a front (secondary) service reservoir 114 and a rear (or primary) service reservoir 116. The front service reservoir 114 is in fluid communication with a brake valve 118a for engaging the front brake 120 upon the application of compressed air, while the rear service reservoir 116 is in fluid communication with brake valve 118b for engaging the rear brake 122 upon the application of compressed air. Additionally, the front service reservoir 114 is in fluid communication with the park control lever 124 and spring (or parking) brake control valve 126 for engaging the spring brake component 128 of the parking brake; this parking brake is applied when the driver actuates the park control lever 124/spring brake control valve 126 or when the compressed air pressure falls below a preset psi (e.g. 60 psi). As previously described, “pumping down” the brakes to engage this parking brake by reducing the air pressure below this predetermined pressure level results in a number of problems such as unnecessary wear and tear on the brake system and potentially premature brake system failure as well as an unsafe condition whereby the spring brake component/parking break is capable of being released due to residual compressed air in the system.
As such, what is desired is an air drain system which is capable of safely draining the air tanks, as well as draining or removing harmful moisture and oil from the air lines, and which is capable of safely engaging the parking brake system which results in safely securing school buses and other commercial vehicles exhibiting air brakes. Furthermore, an air drain system is desired which allows securing of commercial vehicles without damaging the entire braking system and which is designed to prevent wear and tear on air valves and mechanical parts which is typically exhibited by those brake systems requiring “pumping down” of the brakes.